yes, you have to dam it with stiffer buttercream that you are using for the rest of the cake....also, per sugarshack's instructions, after damming, crumb coat just around the center to seal it in and leave sit for atleast 4 hrs for settling. This way if it does bulge, you can clean it up and it will have settled enough...I have found this to be very helpful..hope that makes sense.

i use thicker buttercream for the filling and then thin it for the crumbcoat. also press down really well on the top of the cake to allow for the bulging to come out and then scrape it away - its the weight of the fondant and also any trapped air between the layers that causes bulging - i very rarely get a bulge now.